The present invention relates to methods of forming groups of articles, e.g. in the case of machines for automatically packaging products such as food products, especially of the type designed to produce multiple packs or xe2x80x9cmultipacksxe2x80x9d as they are known.
This possible application, to which extensive reference will be made in the course of this description, should not however be interpreted as tending to limit the scope of the invention.
In a machine for producing multipacks, the individual articles in the pack (each consisting of an individual product or group of products, such as one or more bars of chocolate already inserted in a pack of the type commonly known as xe2x80x9cflow-packxe2x80x9d) are grouped together and then inserted into another xe2x80x9cflow-packxe2x80x9d pack of larger size. The articles intended to be grouped together are usually fed to the inlet of the machine that forms the multiple packs in the form of a continuous flow of groups of articles running more or less nose-to-tail (even though not necessarily with contact and/or appreciable pushing). In order to produce the multiple pack it is therefore necessary to create, between the groups of articles moving in this continuous flow, regularly spaced gaps or spaces in which the continuous tubular wrapping from which the multipack is to be made can be subjected to the action of the sealing and cutting elements (the so-called xe2x80x9cjawsxe2x80x9d) that produce the closed ends of the individual multipacks.
The approaches traditionally adopted in this field to solve this problem can be broken down into two fundamental versions, namely:
those in which, by different means, empty spaces corresponding to the absence of an article are created in the incoming flow, and
those in which the stream of articles introduced into the tubular wrapping to make the multipack is modified by periodically slowing down one article in n. The number n of course indicates the number of articles included in the group that is to be fed into a single multipack.
The first approach is often found to be rather critical to realize in terms of machinery, chiefly because it is fairly rigid in terms of how it operates. This applies particularly to the possibility of selectively varying (i) the size of the spaces created in the incoming flow, and (ii) the number n of articles included in each group. When this approach is adopted in combination with conveying systems that apply a positive drive to the products (e.g. toothed-chain conveyors in which a tooth or lug drives each conveyed article), the modifications referred to above almost invariably involve replacing parts of the conveyor systemxe2x80x94a factor which is usually most unwelcome to users who wish to be able to vary the modes of operation of the machine (or format change) without having to change parts.
The implementation of the second approach (with slowing down or, more usually, momentarily stopping the flow of incoming articles at selectively determined positions) becomes difficult as the speed of advance of the incoming articles increases. At high speeds the periodic action of slowing or stopping tends to induce bumping, bouncing and misalignment of the articles with consequent loss of the exact positioning required at the moment of insertion into the tubular wrapping defining the multipack.
Document U.S. Pat. No. 6,006,892, used as the model for the preambles of claims 1 and 4, describes yet another approach, in which the groups of articles are formed by a pusher element capable of selectively applying to the articles themselves a pushing action generated by a movement at a speed generally greater than the speed of advance of the articles in the incoming flow. The groups are therefore formed by one article moving towards at least one article situated ahead of it in the said flow.
In particular, the same document describes a mechanism for operating the pusher element that essentially comprises a supporting arm fitted with a first operating arm and a second operating arm, the arrangement being such that the pusher element is given a cyclical movement along a roughly ellipsoidal path.
Though operating perfectly satisfactorily, the approach described in the abovementioned document is capable of further improvement from at least two points of view, namely:
the ability to operate over a wide range of possible values for the number n of articles included in each group, and
the ability to carry out the format-change function completely automatically (in practice, simply by acting on the electronic control unit of the mechanism) without the need for modifying or replacing parts of the mechanism.
It is an object of the present invention to provide a solution capable of realizing the abovementioned improvements.
According to the present invention, the possible field of application of which is not however limited to the particular sector referred to above, this object is achieved by means of a process having the further characteristics claimed specifically in the appended claims.
The invention also refers to a corresponding device.
While on the subject, it should be noted that the device according to the invention is equally suitable both for carrying out the process described above and for performing processes involving forming groups of more conventional type, e.g. on the principles described in document U.S. Pat. No. 6,006,892 already referred to earlier and in the prior art cited in that document.